The photorefractive effect involves light-induced charge redistribution in a nonlinear optical material which produces local changes in the index of refraction such that dynamic, erasable holograms can be formed which diffract light. The photorefractive effect is achieved by exposing the material to an optical intensity pattern consisting of bright and dark regions, such as formed by interfering two coherent laser writing beams. Mobile charge generated in the material migrates to the appropriate region to form internal space charge electric fields which diffract the light during readout with a reading beam in accordance with the electro-optic effect
Inorganic crystals exhibiting the photorefractive effect are well known in the art as described in Guenter and Huignard "Photorefractive Materials and Their Applications", Vol. I and II ("Topics in Applied Physics" Vols. 61 and 62) (Springer, Berlin, Heidelberg 1988), the disclosure of which is incorporated herein by reference. Inorganic photorefractive crystals have been fabricated into optical articles for the transmission and control (change phase, intensity, or direction of propagation) of electromagnetic radiation.
Solid State Communications Vol. 74, pages 867-870, 1990 discloses organic crystals of 2-cyclooctylamino-5-nitropyridinedoped with a minor amount of 7,7,8,8-tetracyanoquinodimethane which apparently show the photorefractive effect.
However, it is technically difficult to fabricate such crystals into desired thin layered devices such as optical wave guides. Further, it is difficult to dope organic crystalline material with dopants to achieve desired property improvements such as increase in the speed and/or magnitude of the photorefractive effect because dopants are often excluded from the crystals during growth.
Therefore, there still is a need in the art for photorefractive materials which can be readily fabricated into thin film optical devices and can be doped with sufficient amounts of suitable dopants to achieve desired property improvements.
It is therfore an object of this invention to provide a processable polymeric material exhibiting a photorefractive effect.
Other objects and advantages will become apparent from the following disclosure.